Synthetic aperture ladar motion compensation method based on symmetrical triangular linear frequency modulation continuous wave

Abstract

Synthetic Aperture Ladar (SAL) has the ability to achieve fast high-resolution imaging due to the characteristics of ultra-high resolution and ultra-short synthetic aperture time. However, because synthetic aperture ladar operates in the near-infrared band and the operating wavelength is extremely short, small variations in flightpath can produce artifacts in the phase history that corrupt SAL image generation. This work proposes a motion compensation method based on symmetrical triangular linear frequency modulation continuous wave (T-FMCW) combining with Phase Gradient Autofocus (PGA). Firstly, the ambiguity function of T-FMCW is deduced and its characteristics are analyzed. Then the principle of velocity measurement and Cramer–Rao lower bound of speed estimation error based on this waveform are given. T-FMCW is used to estimate the radial velocity error of the platform in SAL system, and then the radial motion error is estimated by integration along azimuth to realize coarsely focused SAL image. For the coarsely focused SAL image, the residual motion error is extracted to improve the image quality by using PGA. The effectiveness and accuracy of the method is verified by simulation experiments.